1. Field of the Invention
The present invention relates generally to stair structures and in particular to brackets for constructing stair stringer assemblies.
2. Description of the Prior Art
Various types of stair structures are well known in the construction industry and generally include a plurality of horizontal treads supported at regularly-spaced horizontal and vertical intervals. Vertical panels referred to as risers are sometimes placed between adjacent pairs of treads. The treads and risers may be supported by inclined beams, which are commonly referred to as stringers. In a stair structure comprising a single, straight flight of stairs extending between the floors of a building, the stringers may span a considerable distance and support a substantial load.
In residential wood-frame construction, the stringers are often formed from 2.times.12's, i.e. lumber with a nominal thickness of 2 inches and a nominal width of 12 inches respectively. Typically, the stringers are notched to provide a series of stair-stepped, horizontal edges for supporting the treads. However, a problem with this type of construction is that the notches significantly weaken the stringers. For example, many residential building codes now require a minimum of 11 inches for the tread depth (measured front-to-back) and a maximum of 7 inches for the riser height. A 2.times.12 stringer notched to meet these minimums is reduced to a minimum width of about 5 to 6 inches, or about one-half of its original width. Thus, conventional, notched stringers tend to be relatively weak and subject to deflection when loaded. Since building codes generally require that stairs be capable of supporting certain minimum loads without deflecting more than a given amount, conventional stringers must often be supported in mid-span.
Another problem with conventional stringers formed in this manner is that the 2.times.12's are relatively expensive compared to other sizes of structural lumber. One reason is that much larger trees are required to produce 2.times.12's than, for example, 2.times.6's, whereby the former tend to command a premium price per board foot. Since a substantial amount of the structural strength of a 2.times.12 is lost when it is notched for use as a stringer, conventional stringer construction practice represents a relatively inefficient use of timber resources and a relatively costly method of constructing stairs.
The Phillips U.S. Pat. No. 2,724,466 shows a stair construction comprising metal brackets bolted together with treads and risers fastened thereto. Although this arrangement avoids some of the aforementioned shortcomings of conventional stairs with notched stringers, it is relatively complex and is not particularly well-suited for spanning relatively long distances since it lacks a structural member functioning as a beam.
Step brackets for mounting on un-notched stringers are shown in the Dean U.S. Pat. No. 4,015,687. The brackets are attached to the top edges of stringers and to the bottom faces of treads. However, they offer little resistance to lateral forces and they might be difficult to utilize in certain stairs because of the conditions encountered at the top and the bottom.
Another stairway with un-notched stringers is shown in the Crepeau U.S. Pat. No. 4,464,870 wherein the treads are notched to receive the risers and both are toenailed to the top edges of the stringers. However, this construction requires relatively precise joinery of the treads and risers and also requires carefully calculating the dimensions of each in order to have the treads evenly spaced and level.
Heretofore, there have not been available brackets for stair structures with the advantages and features of the present invention.